1. Field of the Invention
The present invention generally relates to a magnetoresistance effect element and a method for producing the same.
2. Description of Related Art
In recent years, the density of information recorded in a magnetic recording medium has been increased. In HDD (Hard Disk Drive) units, a system having a high packing density of 10 Gbpsi (Gigabit per square inch) has been put to practical use, and a system having a higher packing density has been required. As a countermeasure thereto, it is important to form a narrow track having a width of 1 μm in a magnetic head. Also in a recording and/or reproducing thin-film magnetic head, various proposals for structure have been made in order to achieve a narrow track. However, it is said that a magnetic packing density capable of being applied to the structure of a conventionally proposed recording and/or reproducing thin-film magnetic head is limited to about 100 to 200 Gbpsi. In order to further increase the magnetic packing density, it is required to provide a magnetic gap having a size of 0.1 μm or less and a high reproducing output. However, it is very difficult to realize such a magnetic gap and a high reproducing output in a conventionally proposed recording and/or reproducing thin-film magnetic head.
Therefore, in order to solve these problems, a horizontal thin-film magnetic head and a CPP (Current Perpendicular to the Plane) type magnetoresistance effect film material having a large magnetoresistance effect have been proposed in Japanese Patent Laid-Open Nos. 11-120509 and 11-25433 and Outline of 24-th Lecture of Japan Applied Magnetism Institution (2000), page 427.
FIG. 5 is a schematic diagram most simply showing a CPP type magnetoresistance effect element (which will be also hereinafter referred to as a CPP element). That is, this CPP element 40 has a structure wherein a bottom electrode 41 and a top electrode 45 are formed on the top and bottom of a CPP type magnetoresistance effect film 43, an insulator (not shown) being formed around the bottom and top electrodes 41 and 45. Because of such a structure, a reproducing current I caused to flow through the bottom electrode 41 is separated into a current 11 flowing through the CPP type magnetoresistance effect film 43 and a leakage current 12 flowing between the top and bottom electrodes 41 and 45 to flow into the top electrode 45. At this time, with respect to the output of the CPP type magnetoresistance effect film 43, only a variation in resistance due to the current 11 is detected as a variation in voltage.
In the thin-film magnetic head using the CPP element 40 wherein a current is applied in a direction perpendicular to the plane of the film, the thickness of the insulator decreases as the thickness of the reproducing element (CPP element) decreases. In accordance therewith, the distance between the electrodes 41 and 45 for sandwiching the reproducing element therebetween decreases, and the possibility of increasing a leakage current flowing through the insulator other than a current flowing through the reproducing element increases. Therefore, in order to solve such a problem, it is required to develop a CPP type magnetoresistance effect film material capable of obtaining a high reproducing output with a small current and an insulating material having a high withstand voltage. However, it is not easy to achieve the purposes therefor.
FIG. 6 shows the cross-sectional structure of an actual reproducing magnetic head when the CPP element 40 is applied to the head. In the construction of the reproducing magnetic head, magnetization information is sucked up from a medium (not shown) by a reproducing magnetic yoke 38 to be propagated to the CPP element 40, and the resistance changes by the change in direction of magnetization at that time. In FIG. 6, a magnetization fixing layer 47 is formed on the side portion of the CPP type magnetoresistance effect film 43. Also in this case, in FIG. 6, when a reproducing current is caused to flow, the direction of magnetization of the CPP element 40 fluctuates by a magnetic field due to current from a corner portion of the top electrode 45, so that it is not possible to obtain a high reproducing output.
On the other hand, as a magnetoresistance effect element using the same principle as that of the CPP element, there is a TMR (Tunneling Magneto-Resistance) element. In the case of the TMR element, an insulator of Al2O3 or the like is used as a junction. Since this insulator has a very small thickness of about 1 nm, it is not required to cause a sense current, which flows through the TMR element, to be larger than that of the CPP element, and it is not required to increase the withstand voltage of a surrounding insulator in the TMR element.
On the other hand, it is required to cause a large sense current to flow through the CPP element 40 in order to obtain a high reproducing output. In this case, the magnetic field due to sense current is very large to disturb the direction of magnetization of the magnetization fixing layer 47 and to form the CPP type magnetoresistance effect film 43. Since the direction of magnetization of a magneto-sensitive layer having magnetization disperses, there is a problem in that the detection sensitivity greatly decreases. As an example, the relationship between the sense currents of a TMC element and CPP element and the magnetic fields due to the currents is shown in FIG. 7. As shown in FIG. 7, in order to obtain a necessary and sufficient reproducing output, the sense current of the CPP element must be about ten times as large as that of the TMR element. In accordance therewith, the magnetic field due to current, which is applied to the CPP element and which is produced in the vicinity of the CPP element is a very large magnetic field of 50 to 1000 times as large as that of the TMR element.